There is no way to sort the selected items inside the MultiSelect.
It would be nice to have such functionality implemented or provide an implementation that can achieve the described functionality.
Currently, the relation between the MultiSelect input and its TagList element (the one that holds the selected items) is established with an aria-describedby attribute. That results in the screen readers to report the selection (all selected items) as one line of text which doesn't adequately describe the control or and its context. The text of each selected item is announced but it is not clear how many items are selected. Also, there is no articulation between each item text that is announced.
Consider and implement better relation/structure, so that the context of the widget (the selected items and their number) is announced clearly.